How to convert array of nested objects to CSV?

I have an array with nested objects, such as this one:

[
    {"name": "1", "children": [{"name": "1.1", "children":"1.2"}]},
    {"id": "2", "thing": [{"name": "2.1", "children":"2.2"}]},
    {"name": "3", "stuff": [{"name": "3.1", "children":"3.2"}]},
]

The objects can contain values of different types, including other, nested objects.

I want to convert this array to CSV format.

I've tried to iterate with for .. in loops, regular nested for loops, .map() and recursion. I think recursion might be the only way to solve this particular problem, though. For the CSV field names I want to use the sequence of keys that lead to the value.

For the given example, the CSV result I'm looking for is:

name, children.name, children.children,id, thing.name, thing.children,  stuff.name, stuff.children
1, 1.1, 1.2,
,,,2,2.1,2.2
3,,,,3,3.1,3.2

Solution

You could use this ES6 function to create the 2D array you are looking for, which you can then easily transform to CSV:

function pivot(arr) {
    var mp = new Map();
    
    function setValue(a, path, val) {
        if (Object(val) !== val) { // primitive value
            var pathStr = path.join('.');
            var i = (mp.has(pathStr) ? mp : mp.set(pathStr, mp.size)).get(pathStr);
            a[i] = val;
        } else {
            for (var key in val) {
                setValue(a, key == '0' ? path : path.concat(key), val[key]);
            }
        }
        return a;
    }
    
    var result = arr.map( obj => setValue([], [], obj) );
    return [[...mp.keys()], ...result];
}

function toCsv(arr) {
    return arr.map( row => 
        row.map ( val => isNaN(val) ? JSON.stringify(val) : +val ).join(',')
    ).join('\n');
}

// Sample data
var arr = [
    {"name": "1", "children": [{"name": "1.1", "children":"1.2"}]},
    {"id": "2", "thing": [{"name": "2.1", "children":"2.2"}]},
    {"name": "3", "stuff": [{"name": "3.1", "children":"3.2"}]},
];

// Conversion to 2D array and then to CSV:
console.log(toCsv(pivot(arr)));

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For other ways to convert a 2D array to CSV, see this Q&A.